Level indicators are the most common elements in automatic control systems. These devices allow us to visualise the liquid level of any container, so that we can design automatic liquid inlet closing or opening systems or simply obtain first line information on how full a container is. Next, we will see how to make a water level indicator with a simple electronic circuit.
- 560k Ω resistors (eight in total).
- 10k Ω resistors (eight in total).
- 8 red led's of 5mm.
- An integrated type ULN2803.
- A switch.
- Acrylic rods.
- Container or tank.
- 12 V power supply.
Creating our level indicator
To begin, we are going to place several conductive connections (in our case the screws) inside the vessel or tank, fixed with small acrylic bars, so that we can place the indicator sensors at different levels of liquid inside the vessel. Once the sensors are in place, using a tin soldering iron, we create connections from each of the sensors to the outside of the vessel using wires.
Also, we must place a common connection for all the sensors, which will go from the bottom of the container to connection No. 10 of the ULN2803 circuit. Each of the connections of the rest of the sensors will go from connection 1 to connection 7 of the ULN2803, previously passing through a 10 KΩ resistor.
Then, we connect the outputs of the integrated connections from connection 18 to connection 11, to 560 KΩ resistors, and from there to each of the LEDs. Then, we make a connection between all the LEDs and the parallel circuit line that is common for all the tips.
Next, we make the test connection directly to the 12 V power supply.
How it works
When the water reaches the level where one of the sensors is located, an electrical connection is created between the common connection for all the sensors and the water level. This junction closes a circuit, sending the energy necessary to switch on the LED that indicates the water level.
If the water level covers several sensors, as many LED's will light up as sensors are covered, thus giving us an idea of the liquid level inside a tank. In this experiment, we use a switch to increase the safety of the circuit and save energy, but it can also work directly.